1 /* SPDX-License-Identifier: LGPL-2.1 OR MIT */ 2 /* 3 * rseq-arm.h 4 * 5 * (C) Copyright 2016-2022 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com> 6 */ 7 8 /* 9 * - ARM little endian 10 * 11 * RSEQ_SIG uses the udf A32 instruction with an uncommon immediate operand 12 * value 0x5de3. This traps if user-space reaches this instruction by mistake, 13 * and the uncommon operand ensures the kernel does not move the instruction 14 * pointer to attacker-controlled code on rseq abort. 15 * 16 * The instruction pattern in the A32 instruction set is: 17 * 18 * e7f5def3 udf #24035 ; 0x5de3 19 * 20 * This translates to the following instruction pattern in the T16 instruction 21 * set: 22 * 23 * little endian: 24 * def3 udf #243 ; 0xf3 25 * e7f5 b.n <7f5> 26 * 27 * - ARMv6+ big endian (BE8): 28 * 29 * ARMv6+ -mbig-endian generates mixed endianness code vs data: little-endian 30 * code and big-endian data. The data value of the signature needs to have its 31 * byte order reversed to generate the trap instruction: 32 * 33 * Data: 0xf3def5e7 34 * 35 * Translates to this A32 instruction pattern: 36 * 37 * e7f5def3 udf #24035 ; 0x5de3 38 * 39 * Translates to this T16 instruction pattern: 40 * 41 * def3 udf #243 ; 0xf3 42 * e7f5 b.n <7f5> 43 * 44 * - Prior to ARMv6 big endian (BE32): 45 * 46 * Prior to ARMv6, -mbig-endian generates big-endian code and data 47 * (which match), so the endianness of the data representation of the 48 * signature should not be reversed. However, the choice between BE32 49 * and BE8 is done by the linker, so we cannot know whether code and 50 * data endianness will be mixed before the linker is invoked. So rather 51 * than try to play tricks with the linker, the rseq signature is simply 52 * data (not a trap instruction) prior to ARMv6 on big endian. This is 53 * why the signature is expressed as data (.word) rather than as 54 * instruction (.inst) in assembler. 55 */ 56 57 #ifdef __ARMEB__ 58 #define RSEQ_SIG 0xf3def5e7 /* udf #24035 ; 0x5de3 (ARMv6+) */ 59 #else 60 #define RSEQ_SIG 0xe7f5def3 /* udf #24035 ; 0x5de3 */ 61 #endif 62 63 #define rseq_smp_mb() __asm__ __volatile__ ("dmb" ::: "memory", "cc") 64 #define rseq_smp_rmb() __asm__ __volatile__ ("dmb" ::: "memory", "cc") 65 #define rseq_smp_wmb() __asm__ __volatile__ ("dmb" ::: "memory", "cc") 66 67 #define rseq_smp_load_acquire(p) \ 68 __extension__ ({ \ 69 rseq_unqual_scalar_typeof(*(p)) ____p1 = RSEQ_READ_ONCE(*(p)); \ 70 rseq_smp_mb(); \ 71 ____p1; \ 72 }) 73 74 #define rseq_smp_acquire__after_ctrl_dep() rseq_smp_rmb() 75 76 #define rseq_smp_store_release(p, v) \ 77 do { \ 78 rseq_smp_mb(); \ 79 RSEQ_WRITE_ONCE(*(p), v); \ 80 } while (0) 81 82 #define __RSEQ_ASM_DEFINE_TABLE(label, version, flags, start_ip, \ 83 post_commit_offset, abort_ip) \ 84 ".pushsection __rseq_cs, \"aw\"\n\t" \ 85 ".balign 32\n\t" \ 86 __rseq_str(label) ":\n\t" \ 87 ".word " __rseq_str(version) ", " __rseq_str(flags) "\n\t" \ 88 ".word " __rseq_str(start_ip) ", 0x0, " __rseq_str(post_commit_offset) ", 0x0, " __rseq_str(abort_ip) ", 0x0\n\t" \ 89 ".popsection\n\t" \ 90 ".pushsection __rseq_cs_ptr_array, \"aw\"\n\t" \ 91 ".word " __rseq_str(label) "b, 0x0\n\t" \ 92 ".popsection\n\t" 93 94 #define RSEQ_ASM_DEFINE_TABLE(label, start_ip, post_commit_ip, abort_ip) \ 95 __RSEQ_ASM_DEFINE_TABLE(label, 0x0, 0x0, start_ip, \ 96 (post_commit_ip - start_ip), abort_ip) 97 98 /* 99 * Exit points of a rseq critical section consist of all instructions outside 100 * of the critical section where a critical section can either branch to or 101 * reach through the normal course of its execution. The abort IP and the 102 * post-commit IP are already part of the __rseq_cs section and should not be 103 * explicitly defined as additional exit points. Knowing all exit points is 104 * useful to assist debuggers stepping over the critical section. 105 */ 106 #define RSEQ_ASM_DEFINE_EXIT_POINT(start_ip, exit_ip) \ 107 ".pushsection __rseq_exit_point_array, \"aw\"\n\t" \ 108 ".word " __rseq_str(start_ip) ", 0x0, " __rseq_str(exit_ip) ", 0x0\n\t" \ 109 ".popsection\n\t" 110 111 #define RSEQ_ASM_STORE_RSEQ_CS(label, cs_label, rseq_cs) \ 112 RSEQ_INJECT_ASM(1) \ 113 "adr r0, " __rseq_str(cs_label) "\n\t" \ 114 "str r0, %[" __rseq_str(rseq_cs) "]\n\t" \ 115 __rseq_str(label) ":\n\t" 116 117 #define RSEQ_ASM_CMP_CPU_ID(cpu_id, current_cpu_id, label) \ 118 RSEQ_INJECT_ASM(2) \ 119 "ldr r0, %[" __rseq_str(current_cpu_id) "]\n\t" \ 120 "cmp %[" __rseq_str(cpu_id) "], r0\n\t" \ 121 "bne " __rseq_str(label) "\n\t" 122 123 #define __RSEQ_ASM_DEFINE_ABORT(table_label, label, teardown, \ 124 abort_label, version, flags, \ 125 start_ip, post_commit_offset, abort_ip) \ 126 ".balign 32\n\t" \ 127 __rseq_str(table_label) ":\n\t" \ 128 ".word " __rseq_str(version) ", " __rseq_str(flags) "\n\t" \ 129 ".word " __rseq_str(start_ip) ", 0x0, " __rseq_str(post_commit_offset) ", 0x0, " __rseq_str(abort_ip) ", 0x0\n\t" \ 130 ".word " __rseq_str(RSEQ_SIG) "\n\t" \ 131 __rseq_str(label) ":\n\t" \ 132 teardown \ 133 "b %l[" __rseq_str(abort_label) "]\n\t" 134 135 #define RSEQ_ASM_DEFINE_ABORT(table_label, label, teardown, abort_label, \ 136 start_ip, post_commit_ip, abort_ip) \ 137 __RSEQ_ASM_DEFINE_ABORT(table_label, label, teardown, \ 138 abort_label, 0x0, 0x0, start_ip, \ 139 (post_commit_ip - start_ip), abort_ip) 140 141 #define RSEQ_ASM_DEFINE_CMPFAIL(label, teardown, cmpfail_label) \ 142 __rseq_str(label) ":\n\t" \ 143 teardown \ 144 "b %l[" __rseq_str(cmpfail_label) "]\n\t" 145 146 /* Per-cpu-id indexing. */ 147 148 #define RSEQ_TEMPLATE_CPU_ID 149 #define RSEQ_TEMPLATE_MO_RELAXED 150 #include "rseq-arm-bits.h" 151 #undef RSEQ_TEMPLATE_MO_RELAXED 152 153 #define RSEQ_TEMPLATE_MO_RELEASE 154 #include "rseq-arm-bits.h" 155 #undef RSEQ_TEMPLATE_MO_RELEASE 156 #undef RSEQ_TEMPLATE_CPU_ID 157 158 /* Per-mm-cid indexing. */ 159 160 #define RSEQ_TEMPLATE_MM_CID 161 #define RSEQ_TEMPLATE_MO_RELAXED 162 #include "rseq-arm-bits.h" 163 #undef RSEQ_TEMPLATE_MO_RELAXED 164 165 #define RSEQ_TEMPLATE_MO_RELEASE 166 #include "rseq-arm-bits.h" 167 #undef RSEQ_TEMPLATE_MO_RELEASE 168 #undef RSEQ_TEMPLATE_MM_CID 169 170 /* APIs which are not based on cpu ids. */ 171 172 #define RSEQ_TEMPLATE_CPU_ID_NONE 173 #define RSEQ_TEMPLATE_MO_RELAXED 174 #include "rseq-arm-bits.h" 175 #undef RSEQ_TEMPLATE_MO_RELAXED 176 #undef RSEQ_TEMPLATE_CPU_ID_NONE 177